U.S. patent number 11,141,587 [Application Number 16/295,145] was granted by the patent office on 2021-10-12 for system, method, and apparatus for applying transcutaneous electrical stimulation.
This patent grant is currently assigned to AVATION MEDICAL, INC.. The grantee listed for this patent is AVATION MEDICAL, INC.. Invention is credited to Alexandru Campean, Jeff A. Weisgarber, Mingming Zhang.
United States Patent |
11,141,587 |
Campean , et al. |
October 12, 2021 |
System, method, and apparatus for applying transcutaneous
electrical stimulation
Abstract
A system, method, and apparatus for treating a medical condition
by applying transcutaneous electrical stimulation to a target
peripheral nerve of a subject. Electrical stimulation is applied to
the peripheral nerve via a stimulation electrode pattern under
closed-loop control in which EMG responses are monitored and used
to adjust stimulation parameters. In response to detecting an
unacceptable recording, electrical stimulation is applied to the
peripheral nerve under open-loop control.
Inventors: |
Campean; Alexandru
(Strongsville, OH), Weisgarber; Jeff A. (Jewett, OH),
Zhang; Mingming (Hilliard, OH) |
Applicant: |
Name |
City |
State |
Country |
Type |
AVATION MEDICAL, INC. |
Columbus |
OH |
US |
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Assignee: |
AVATION MEDICAL, INC.
(Columbus, OH)
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Family
ID: |
65818689 |
Appl.
No.: |
16/295,145 |
Filed: |
March 7, 2019 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20200069942 A1 |
Mar 5, 2020 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62725755 |
Aug 31, 2018 |
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62751173 |
Oct 26, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N
1/36031 (20170801); A61N 1/0484 (20130101); A61N
1/0456 (20130101); A61B 5/053 (20130101); A61N
1/36007 (20130101); A61B 5/7221 (20130101); A61N
1/36021 (20130101); A61B 5/389 (20210101); A61N
1/0452 (20130101); A61N 1/36003 (20130101) |
Current International
Class: |
A61N
1/36 (20060101); A61B 5/389 (20210101); A61N
1/04 (20060101); A61B 5/00 (20060101); A61B
5/053 (20210101) |
Field of
Search: |
;607/39 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2013/071307 |
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May 2013 |
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WO |
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2014/003633 |
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Jan 2014 |
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WO |
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Other References
Austrialian Examination Report for corresponding Australian
Application Serial No. 2019333201, dated Aug. 17, 2021, pp. 1-2.
cited by applicant.
|
Primary Examiner: Hulbert; Amanda K
Assistant Examiner: Edwards; Philip C
Attorney, Agent or Firm: Tarolli, Sundheim, Covell &
Tummino LLP
Parent Case Text
RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application
Ser. No. 62/725,755, filed on Aug. 31, 2018. This application also
claims the benefit of U.S. Provisional Application Ser. No.
62/751,173, filed on Oct. 26, 2018. The subject matter of these
applications is hereby incorporated by reference in its entirety.
Claims
We claim:
1. A method for treating a medical condition by applying
transcutaneous electrical stimulation to a target peripheral nerve
of a subject, comprising: positioning a plurality of stimulation
electrodes on a skin surface proximate the targeted peripheral
nerve, the stimulation electrodes being spaced from each other in a
predetermined configuration; positioning one or more recording
electrodes on a skin surface remote from the stimulation electrodes
at a location where electromyogram (EMG) responses to electrical
stimulation of the targeted peripheral nerve can be detected;
selecting a stimulation electrode pattern from a pattern list; and
applying electrical stimulation pulses via the selected stimulation
electrode pattern, wherein the pattern list being determined by: a)
identifying a set of predetermined stimulation electrode patterns,
each stimulation electrode pattern identifying which of the
plurality of stimulation electrodes will apply the electrical
stimulation pulses, and each stimulation electrode pattern having
associated with it stimulation parameters according to which it
applies stimulation pulses; b) selecting a stimulation electrode
pattern from the set of predetermined stimulation electrode
patterns; c) generating a stimulation pulse using the selected
stimulation electrode pattern according to its associated
stimulation parameters; d) determining via the recording electrodes
whether the stimulation pulse using the selected stimulation
electrode pattern elicited an EMG response; e) adding the selected
stimulation electrode pattern to the pattern list in response to
detecting an EMG response; f) omitting the selected stimulation
electrode pattern from the pattern list in response to not
detecting an EMG response; and repeating steps b) through f) for
each stimulation electrode pattern in the set of predetermined
stimulation electrode patterns to complete the pattern list.
2. The method recited in claim 1, further comprising optimizing the
stimulation electrode patterns in the pattern list by: adjusting
the stimulation parameters for each stimulation electrode pattern
in the pattern list to attempt to elicit an improved EMG response;
g) selecting a stimulation electrode pattern from the set of
predetermined stimulation electrode patterns; h) generating a
stimulation pulse using the selected stimulation electrode pattern
according to its associated stimulation parameters; i) determining
via the recording electrodes whether the stimulation pulse using
the selected stimulation electrode pattern elicited an EMG
response; j) adding the selected stimulation electrode pattern to
the pattern list in response to detecting an EMG response; k)
omitting the selected stimulation electrode pattern from the
pattern list in response to not detecting an EMG response; and
repeating steps g) through k) for each stimulation electrode
pattern in the set of predetermined stimulation electrode patterns
to complete the pattern list.
3. The method recited in claim 2, further comprising repeating the
steps of claim 2 until each electrode pattern in the pattern list
is optimized.
4. The method recited in claim 1, further comprising ordering the
stimulation electrode patterns in the pattern list according to
their elicited EMG responses.
5. The method recited in claim 1, wherein applying electrical
stimulation pulses via the selected stimulation electrode pattern
comprises: stimulating the peripheral nerve by applying electrical
stimulation pulses via a stimulation electrode pattern selected
from the plurality of stimulation electrodes according to
stimulation parameters under closed-loop control in which EMG
responses to the electrical stimulation pulses are monitored via
the recording electrodes and the stimulation parameters are
adjusted in response to the monitored EMG responses; and in
response to detecting an unacceptable condition of the recording
electrodes, applying electrical stimulation pulses via the
stimulation electrode pattern according to the stimulation
parameters under open-loop control in which the stimulation
parameters are maintained without adjustment.
6. The method recited in claim 5, wherein the unacceptable
condition of the recording electrodes comprises unacceptable
impedance measurements.
7. The method recited in claim 5, wherein the step of applying
electrical stimulation pulses further comprises monitoring for
mechanomyogram (MMG) responses to the electrical stimulation pulses
and applying the electrical stimulation pulses under closed-loop
control in which the stimulation parameters are adjusted in
response to the monitored MMG responses.
8. The method recited in claim 5, wherein the step of applying
electrical stimulation pulses comprises detecting impedances of the
recording electrodes and, in response to detecting acceptable
impedances of the recording electrodes, applying the electrical
stimulation pulses.
9. The method recited in claim 5, wherein applying electrical
stimulation pulses via the selected stimulation electrode pattern
further comprises: obtaining sample measurements via the recording
electrodes; checking the sample measurements for noise; checking
the sample measurements for voluntary EMG responses; applying the
electrical stimulation pulses under closed-loop control in response
to determining an acceptable level of noise and the absence of
voluntary EMG responses; and applying the electrical stimulation
pulses under open-loop control in response to determining an
unacceptable level of noise or the presence of voluntary EMG
responses.
10. The method recited in claim 5, wherein each application of an
electrical stimulation pulse under closed-loop control comprises:
applying the electrical stimulation pulse; executing a time delay;
recording EMG responses via the recording electrodes after the time
delay is executed; and adjusting the stimulation parameters in
response to the recorded EMG responses.
11. The method recited in claim 10, wherein the duration of the
time delay is about 5 ms or less.
12. The method recited in claim 10, wherein adjusting the
stimulation parameters in response to the recorded EMG responses
under closed loop control comprises: increasing the amplitude of
subsequent stimulation pulses in response to the recorded EMG
responses being below a predetermined EMG window; decreasing the
amplitude of subsequent stimulation pulses in response to the
recorded EMG responses being above the predetermined EMG window;
and maintaining the amplitude of subsequent stimulation pulses in
response to the recorded EMG responses being within the
predetermined EMG window.
13. The method recited in claim 5, wherein each application of an
electrical stimulation pulse under open-loop control comprises:
applying the electrical stimulation pulse; and executing a time
delay having a duration sufficient to maintain a constant
stimulation period.
14. The method recited in claim 13, wherein the duration of the
time delay is about 75 ms.
15. The method recited in claim 5, wherein stimulating the
peripheral nerve comprises stimulating the tibial nerve.
16. The method recited in claim 5, wherein stimulating the
peripheral nerve comprises stimulating the tibial nerve at a
location between the medial malleolus and the Achilles tendon.
17. The method recited in claim 5, wherein monitoring EMG responses
comprises recording EMG signals that result from recruitment of the
tibial nerve's motor fibers.
18. The method recited in claim 5, wherein monitoring EMG responses
comprises positioning the recording electrodes on the bottom of the
subject's foot near the abductor hallucis and the flexor hallucis
brevis to record the EMG signals.
19. The method recited in claim 5, wherein stimulating the
peripheral nerve comprises stimulating the tibial nerve to treat
overactive bladder, sexual dysfunction, or plantar fasciitis.
20. The method recited in claim 5, wherein stimulating the
peripheral nerve comprises stimulating the ulnar nerve and/or
median nerve for pain management in carpal tunnel syndrome,
hypertension management, and nerve conduction study/nerve injury
diagnosis for median/ulnar nerve neuropathy.
21. The method recited in claim 5, wherein stimulating the
peripheral nerve comprises stimulating the ulnar nerve and/or
median nerve to treat carpal tunnel syndrome or hypertension.
22. The method recited in claim 5, wherein stimulating the
peripheral nerve comprises stimulating the ulnar nerve and/or
median nerve to perform a nerve conduction study or nerve injury
diagnosis.
23. The method recited in claim 5, wherein: stimulating the ulnar
nerve and/or median nerve comprises positioning the stimulating
electrodes on the inside of the lower arm 0 to 20 cm from the wrist
line; and recording EMG responses comprises positioning the
recording electrodes on the base of thumb to record signal from
abductor/flexor pollicis brevis, and/or positioning the recording
electrodes on the base of pinky to record signal from
abductor/flexor digiti minimi brevis.
24. The method recited in claim 5, wherein stimulating the
peripheral nerve comprises applying the electrical stimulation
pulses to the peripheral nerve to enhance nerve regeneration after
peripheral nerve injury.
25. A system for treating overactive bladder by applying
transcutaneous electrical stimulation to the tibial nerve of a
subject, comprising: a plurality of electrical stimulation
electrodes, the stimulation electrodes being spaced from each other
in a predetermined configuration on a skin surface proximate the
tibial nerve; one or more recording electrodes positioned on a skin
surface remote from the stimulation electrodes at a location where
electromyogram (EMG) responses to electrical stimulation of the
tibial nerve can be detected; a structure for supporting the
stimulation electrodes and the recording electrodes spaced apart
from each other in their respective positions; and a control unit
for controlling the operation of the stimulation electrodes and the
recording electrodes, wherein the control unit is configured to:
select a stimulation electrode pattern from a pattern list; and
apply electrical stimulation pulses via the selected stimulation
electrode pattern, wherein the pattern list is determined by: a)
identify a set of predetermined stimulation electrode patterns,
each stimulation electrode pattern identifying which of the
plurality of stimulation electrodes will apply the electrical
stimulation pulses, and each stimulation electrode pattern having
associated with it stimulation parameters according to which it
applies stimulation pulses; b) select a stimulation electrode
pattern from the set of predetermined stimulation electrode
patterns; c) generate a stimulation pulse using the selected
stimulation electrode pattern according to its associated
stimulation parameters; d) determine via the recording electrodes
whether the stimulation pulse using the selected stimulation
electrode pattern elicited an EMG response; e) add the selected
stimulation electrode pattern to the pattern list in response to
detecting an EMG response; f) omit the selected stimulation
electrode pattern from the pattern list in response to not
detecting an EMG response; and repeat steps b) through f) for each
stimulation electrode pattern in the set of predetermined
stimulation electrode patterns to complete the pattern list.
26. The system recited in claim 25, wherein the controller is
configured to apply electrical stimulation pulses via the selected
stimulation electrode pattern by stimulating the peripheral nerve
by applying electrical stimulation pulses via a stimulation
electrode pattern selected from the plurality of stimulation
electrodes according to stimulation parameters under closed-loop
control in which EMG responses to the electrical stimulation pulses
are monitored via the recording electrodes and the stimulation
parameters are adjusted in response to the monitored EMG responses
and, in response to detecting an unacceptable condition of the
recording electrodes, applying electrical stimulation pulses via
the stimulation electrode pattern according to the stimulation
parameters under open-loop control in which the stimulation
parameters are maintained without adjustment.
Description
TECHNICAL FIELD
The invention relates to a wearable electronic medical device for
transcutaneous electrical stimulation of peripheral nerves for the
purpose of treating one or more medical conditions.
BACKGROUND
There are many known technologies that use electrical stimulation
of peripheral nerves to treat medical conditions. Implantable
stimulation technologies require surgical implantation of
stimulation leads, with a pulse generator that is either surgically
implanted or connected externally to wire leads. Percutaneous
stimulation technologies are less invasive, but still require the
stimulation electrodes to pierce the skin. While these technologies
can be effective in treating certain conditions, they are less
desirable due to their invasiveness and because they can require
the continued or routine attention of specialists, requiring
doctor's office visits, phone calls, etc.
SUMMARY
A system for applying transcutaneous electrical stimulation
includes a wearable, such as a garment, sock, sleeve, brace, strap,
etc. The wearable includes an electronic stimulator device that
provides transcutaneous electrical stimulation to peripheral nerves
for treatment of medical conditions. Advantageously, the wearable
allows the subject to use the system at a time and place that is
convenient. The subject may choose to use the device while they are
at work or at home, or while walking, relaxing, or sleeping, as
long as certain environments and/or activities (e.g., wet
environments/activities) are avoided. Since there are no
implantable or percutaneous components, the risk of infection,
battery fault burns, and transcutaneous power transfer discomfort
and/or bleeding, are greatly reduced or eliminated.
The wearable includes electrodes that are arranged in a
predetermined pattern or array, and that engage the subject's skin
at desired locations when the wearable is worn. These skin surface
mounted electrodes can, for example, be similar to those of other
transcutaneous electrical nerve stimulation ("TENS") units to
implement high voltage skin surface electrical stimulation. The
electrodes include stimulating electrodes and recording electrodes,
which the wearable can position at the same location or at
different locations on the subject's skin. In fact, the identities
of individual electrodes, i.e., stimulating or recording, can
change depending on the application/treatment for which the system
is being used. The stimulating electrodes apply the transcutaneous
electrical stimulation to the subject's skin, and the recording
electrodes record the electromyogram (EMG) responses elicited by
the stimulation.
The wearable also includes a control unit that is electrically
connected to the electrodes and that is operable to control
electrical stimulation applied by the stimulating electrodes and to
control the recording of EMG responses by the recording electrodes.
The control unit executes closed-loop control algorithms, which
adjust stimulation patterns, periodically or constantly, based on
the elicited EMG response from the recruited nerves as feedback.
Alternatively, instead of the EMG response providing the
closed-loop feedback, or as a supplement to the EMG response, the
system can include alternative devices, such as mechanomyogram
(MMG) devices (e.g., an accelerometer), or can implement electronic
measurements, such as electrode impedance, to implement the
closed-loop control.
This closed-loop control eliminates the need for "programming
sessions" commonly required for neurostimulation systems. The
day-to-day variability that arises due to electrode placement and
skin impedance necessitates these sessions to make sure that the
electrodes are positioned to provide adequate stimulation
treatment. With the present system, instead of physically adjusting
the electrode positions on the subject in order to find the
arrangement that produces the desired response, the system itself
can select which electrodes to use, and can adjust the number and
pattern of electrodes until an acceptable response (EMG and/or MMG)
is achieved. Once the appropriate electrodes pattern is identified,
the order, intensity, timing, etc. of the stimulation can be
further tuned or adjusted to optimize the EMG and/or MMG response.
The system can tailor the electrical stimulation applied by each
individually controllable electrode in the array so that the
stimulation characteristics of each electrode (e.g., frequency,
amplitude, pattern, duration, etc.) is configured to deliver the
desired stimulation effect. This tailoring can be implemented
automatically through the algorithm, which incrementally adjusts
these characteristics, monitoring the and/or response at each
increment until optimal settings are identified. Stimulation
therapy can then be applied with these settings, according to the
algorithm, which can be dictated by the requirements of the
treating physician.
Throughout the electrical stimulation treatment process, the system
can implement periodic or continuous measurement of system
integrity. One such measurement is that of electrode impedance to
remove the risks that can arise when electrodes lift away from the
skin or certain properties of the electrodes deteriorate. The
impedance measurement capability could also potentially be used to
provide an indication of the optimal electrode location for nerve
stimulation. This may be the case, for example, in areas where the
skin is thin and where the stimulated nerves are most superficial.
Thus, impedance values may be used as an input to the closed-loop
stimulation algorithm to adjust stimulation patterns. By way of
example, when stimulating the tibial nerve, the posterior area of
the medial malleolus typically has comparatively thin skin and is
the site where tibial nerve is most superficial, which leads to its
being a good candidate for measuring electrode impedance.
The control unit and the architecture of the system may be designed
to constantly optimize stimulation by monitoring the quality of
nerve recruitment periodically or on a pulse-by-pulse basis, with
the goal of keeping recruitment strength to a minimum (which can
reduce muscle twitching) and to minimize the stimulation energy
being delivered through the skin. The EMG recording feature is
capable of detecting both M-wave and F-wave responses, which can be
used as feedback inputs (together or independently) to the
closed-loop stimulation algorithm to determine the level of
activation of the stimulated peripheral nerve. A significant aspect
of the F-wave is that it provides an indication that the
stimulation-evoked peripheral nerve action potential has activated
motor neurons in the associated spinal cord nerves/nerve plexus.
For example, an F-wave response to tibial nerve stimulation
indicates that the tibial nerve action potential has activated
motor neurons in the sacral spinal cord/sacral plexus.
The wearable transcutaneous electrical stimulation device can be
used to stimulate various peripheral nerves in order to treat
medical conditions associated with those nerves. For example, the
system can be used to apply electrical stimulation to the tibial
nerve to treat pelvic floor dysfunction, e.g., overactive bladder
(OAB) medical conditions. As another example, the system can be
used to apply electrical stimulation to the tibial nerve to treat
sexual dysfunction. In this manner, it is believed that tibial
nerve stimulation could be used to treat genital arousal aspects of
female sexual interest/arousal disorder by improving pelvic blood
flow. In yet another example, the system can be used to apply
electrical stimulation to the tibial nerve to treat plantar
fasciitis.
As another example, the system can be applied to the wrist area to
provide stimulation to the ulnar nerve and/or median nerve. The
stimulation electrode array can, for example, be placed on the
inside of the lower arm anywhere 0 to 20 cm from the wrist line.
EMG recording electrodes can be placed on the base of thumb to
record signal from abductor/flexor pollicis brevis. EMG recording
electrodes alternatively or additionally can be placed on the base
of pinky to record signal from abductor/flexor digiti minimi
brevis. The nerve activation could be confirmed by recording M-wave
and F-wave EMG signals from the relevant muscles. The EMG signal
can also be used as a control signal to adjust the stimulation
parameters or stimulation electrode patterns. This technology can
be applied to median nerve activation for pain management in carpal
tunnel syndrome, hypertension management, and nerve conduction
study/nerve injury diagnosis for median/ulnar nerve neuropathy,
etc.
As a further example, the system can be used to apply
transcutaneous electrical stimulation to provide neurostimulation
to peripheral nerves in order to enhance nerve regeneration after
peripheral nerve injury.
Implementing closed-loop control, the system can utilize measured
EMG responses to detect and obtain data related to the electrical
activity of muscles in response to the applied stimulation. This
data can be used as feedback to tailor the application of the
electrical stimulation. Additionally or alternatively, the system
can also implement MMG sensors, such as accelerometers, to measure
the physical response of the muscles. Other feedback, such as
impedance measurements between electrodes and other biopotential
recording, can also be utilized. Through this closed-loop
implementation, the system can utilize techniques such as current
steering and nerve localization to provide peripheral nerve
stimulation therapy for treating various medical conditions.
The system, method, and apparatus for applying transcutaneous
electrical stimulation disclosed herein has many aspects, which can
be included or utilized in various combinations.
According to one aspect, a method treats a medical condition by
applying transcutaneous electrical stimulation to a target
peripheral nerve of a subject.
According to another aspect, alone or in combination with any other
aspect, the method can include positioning a plurality of
stimulation electrodes on a skin surface proximate the targeted
peripheral nerve, the stimulation electrodes being spaced from each
other in a predetermined configuration. The method also can include
positioning one or more recording electrodes on a skin surface
remote from the stimulation electrodes at a location where
electromyogram (EMG) responses to electrical stimulation of the
targeted peripheral nerve can be detected. The method also can
include stimulating the peripheral nerve by applying electrical
stimulation pulses via a stimulation electrode pattern selected
from the plurality of stimulation electrodes according to
stimulation parameters under closed-loop control in which EMG
responses to the electrical stimulation pulses are monitored via
the recording electrodes and the stimulation parameters are
adjusted in response to the monitored EMG responses. The method
further can include, in response to detecting an unacceptable
condition of the recording electrodes, applying electrical
stimulation pulses via the stimulation electrode pattern according
to the stimulation parameters under open-loop control in which the
stimulation parameters are maintained without adjustment.
According to another aspect, alone or in combination with any other
aspect, the unacceptable condition of the recording electrodes can
include unacceptable impedance measurements.
According to another aspect, alone or in combination with any other
aspect, the step of applying electrical stimulation pulses further
can include monitoring for mechanomyogram (MMG) responses to the
electrical stimulation pulses and applying the electrical
stimulation pulses under closed-loop control in which the
stimulation parameters are adjusted in response to the monitored
MMG responses.
According to another aspect, alone or in combination with any other
aspect, the step of applying electrical stimulation pulses can
include detecting impedances of the recording electrodes and, in
response to detecting acceptable impedances of the recording
electrodes, applying the electrical stimulation pulses.
According to another aspect, alone or in combination with any other
aspect, the method can include: obtaining sample measurements via
the recording electrodes, checking the sample measurements for
noise, checking the sample measurements for voluntary EMG
responses, applying the electrical stimulation pulses under
closed-loop control in response to determining an acceptable level
of noise and the absence of voluntary EMG responses, and applying
the electrical stimulation pulses under open-loop control in
response to determining an unacceptable level of noise or the
presence of voluntary EMG responses.
According to another aspect, alone or in combination with any other
aspect, each application of an electrical stimulation pulse under
closed-loop control can include: applying the electrical
stimulation pulse, executing a time delay, recording EMG responses
via the recording electrodes after the time delay is executed, and
adjusting the stimulation parameters in response to the recorded
EMG responses. The duration of the time delay can be about 5 ms or
less.
According to another aspect, alone or in combination with any other
aspect, adjusting the stimulation parameters in response to the
recorded EMG responses under closed loop control can include:
increasing the amplitude of subsequent stimulation pulses in
response to the recorded EMG responses being below a predetermined
EMG window, decreasing the amplitude of subsequent stimulation
pulses in response to the recorded EMG responses being above the
predetermined EMG window, and maintaining the amplitude of
subsequent stimulation pulses in response to the recorded EMG
responses being within the predetermined EMG window.
According to another aspect, alone or in combination with any other
aspect, each application of an electrical stimulation pulse under
open-loop control can include: applying the electrical stimulation
pulse, and executing a time delay having a duration sufficient to
maintain a constant stimulation period. The duration of the time
delay can be about 75 ms.
According to another aspect, alone or in combination with any other
aspect, the stimulation electrode pattern can be selected from a
pattern list, wherein the method further can further include
generating the pattern list by: a) identifying a set of
predetermined stimulation electrode patterns, each stimulation
electrode pattern identifying which of the plurality of stimulation
electrodes will apply the electrical stimulation pulses, and each
stimulation electrode pattern having associated with it the
stimulation parameters according to which it applies stimulation
pulses; b) selecting a stimulation electrode pattern from the set
of predetermined stimulation electrode patterns; c) generating a
stimulation pulse using the selected stimulation electrode pattern
according to its associated stimulation parameters; d) determining
via the recording electrodes whether the stimulation pulse using
the selected stimulation electrode pattern elicited an EMG
response; e) adding the selected stimulation electrode pattern to
the pattern list in response to detecting an EMG response; f)
omitting the selected stimulation electrode pattern from the
pattern list in response to not detecting an EMG response; and
repeating steps b) through f) for each stimulation electrode
pattern in the set of predetermined stimulation electrode patterns
to complete the pattern list.
According to another aspect, alone or in combination with any other
aspect, the method can include optimizing the stimulation electrode
patterns in the pattern list by: g) adjusting the stimulation
parameters for each stimulation electrode pattern in the pattern
list to attempt to elicit an improved EMG response; h) selecting a
stimulation electrode pattern from the set of predetermined
stimulation electrode patterns; i) generating a stimulation pulse
using the selected stimulation electrode pattern according to its
associated stimulation parameters; j) determining via the recording
electrodes whether the stimulation pulse using the selected
stimulation electrode pattern elicited an EMG response; k) adding
the selected stimulation electrode pattern to the pattern list in
response to detecting an EMG response; l) omitting the selected
stimulation electrode pattern from the pattern list in response to
not detecting an EMG response; and repeating steps h) through l)
for each stimulation electrode pattern in the set of predetermined
stimulation electrode patterns to complete the pattern list. Steps
h) through l) can be repeated until each electrode pattern in the
pattern list is optimized.
According to another aspect, alone or in combination with any other
aspect, the method can also include ordering the stimulation
electrode patterns in the pattern list according to their elicited
EMG and/or MMG responses.
According to another aspect, alone or in combination with any other
aspect, stimulating the peripheral nerve can include stimulating
the tibial nerve. Stimulating the peripheral nerve can include
stimulating the tibial nerve at a location between the medial
malleolus and the Achilles tendon.
According to another aspect, alone or in combination with any other
aspect, monitoring EMG responses can include recording EMG signals
that result from recruitment of the tibial nerve's motor fibers.
This can include positioning the recording electrodes on the bottom
of the subject's foot near the abductor hallucis and the flexor
hallucis brevis to record the EMG signals.
According to another aspect, alone or in combination with any other
aspect, stimulating the peripheral nerve can treat overactive
bladder, sexual dysfunction, or plantar fasciitis.
According to another aspect, alone or in combination with any other
aspect, stimulating the peripheral nerve can include stimulating
the ulnar nerve and/or median nerve for pain management in carpal
tunnel syndrome, hypertension management, and nerve conduction
study/nerve injury diagnosis for median/ulnar nerve neuropathy,
etc. Stimulating the ulnar nerve and/or median nerve can treat
carpal tunnel syndrome or hypertension. Stimulating the ulnar nerve
and/or median nerve to perform a nerve conduction study or nerve
injury diagnosis.
According to another aspect, alone or in combination with any other
aspect, stimulating the ulnar nerve and/or median nerve can include
positioning the stimulating electrodes on the inside of the lower
arm 0 to 20 cm from the wrist line, and recording EMG responses can
include positioning the recording electrodes on the base of thumb
to record signal from abductor/flexor pollicis brevis, and/or
positioning the recording electrodes on the base of pinky to record
signal from abductor/flexor digiti minimi brevis.
According to another aspect, alone or in combination with any other
aspect, stimulating the peripheral nerve can include applying the
electrical stimulation pulses to the peripheral nerve to enhance
nerve regeneration after peripheral nerve injury.
According to another aspect, alone or in combination with any other
aspect, a system for treating overactive bladder by applying
transcutaneous electrical stimulation to the tibial nerve of a
subject can include a plurality of electrical stimulation
electrodes, the stimulation electrodes being spaced from each other
in a predetermined configuration, one or more recording electrodes,
a structure for supporting the stimulation electrodes and the
recording electrodes spaced apart from each other, and a control
unit for controlling the operation of the stimulation electrodes
and the recording electrodes. The control unit can be configured to
perform the method according to any of the aspects disclosed
herein, alone or in combination with any other aspect.
According to another aspect, alone or in combination with any other
aspect, an apparatus for applying electrical stimulation includes a
plurality of electrical stimulation electrodes spaced from each
other in a predetermined configuration, one or more recording
electrodes, a structure for supporting the stimulation electrodes
and the recording electrodes spaced apart from each other, and a
control unit for controlling the operation of the stimulation
electrodes and the recording electrodes. The control unit is
configured to energize the stimulation electrodes under closed-loop
control using the recording electrodes to measure feedback,
energize the stimulation electrodes under open-loop without
measuring feedback, and determine whether to energize the
stimulation electrodes under closed-loop control or open-loop
control based on determining whether the feedback measured by the
recording electrodes is reliable.
According to another aspect, alone or in combination with any other
aspect, the structure can include a wearable structure configured
to position the stimulation electrodes in the proximity of a
peripheral nerve and to position the recording electrodes in the
proximity of a muscle activated by the peripheral nerve.
According to another aspect, alone or in combination with any other
aspect, the wearable structure can position the stimulation
electrodes proximate the peripheral nerve and the recording
electrodes proximate a location where EMG signals that result from
recruitment of the peripheral nerve's motor fibers can be
detected.
According to another aspect, alone or in combination with any other
aspect, the wearable structure can include a strap, wherein the
stimulation electrodes and recording electrodes are positioned at
different locations along the length of the strap. The strap can be
configured to have a portion wrapped around the subject's ankle to
position the stimulating electrodes proximate the tibial nerve
between the medial malleolus and the Achilles tendon. The strap can
also be configured to have a portion wrapped around the subject's
foot to position the recording electrodes on the bottom of the
subject's foot near the abductor hallucis and the flexor hallucis
brevis.
According to another aspect, alone or in combination with any other
aspect, the wearable structure can include a brace comprising an
upper portion upon which the stimulation electrodes are positioned
and a lower portion upon which the recording electrodes are
positioned. The upper portion of the brace can be configured to be
wrapped around the subject's ankle to position the stimulating
electrodes proximate the tibial nerve between the medial malleolus
and the Achilles tendon. The lower portion of the brace can be
configured to be wrapped around the subject's foot to position the
recording electrodes on the bottom of the subject's foot near the
abductor hallucis and the flexor hallucis brevis.
According to another aspect, alone or in combination with any other
aspect, the apparatus can also include an accelerometer supported
by the support structure adjacent or near the recording electrodes,
wherein the control unit can be configured to determine whether to
energize the stimulation electrodes under closed-loop control or
open-loop control based on acceleration values determined by the
accelerometer.
According to another aspect, alone or in combination with any other
aspect, the control unit can include a microcontroller, a
stimulator output stage controlled by the microcontroller, and at
least one analog output switch operatively connected to the
stimulator output stage and controlled by the microcontroller. The
stimulator output stage can include a plurality of channels for
providing electrical current to the stimulating electrodes via the
output switch, wherein each channel of the output stage includes a
current source and current sink, and wherein the microcontroller is
configured to actuate the output switch to selectively identify
which stimulation electrodes are active and to assign a channel of
the output stage with each active stimulation electrode, wherein
the output stage associated with each stimulating electrode
determines whether the stimulating electrode operates as an anode
or a cathode.
According to another aspect, alone or in combination with any other
aspect, the microcontroller can be configured to determine
amplitude and timing values for the current source and current sink
for each channel of the output stage and their associated active
stimulation electrodes.
According to another aspect, alone or in combination with any other
aspect, the apparatus can include an impedance measurement circuit
that is operatively connected to the stimulator output stage and is
configured to measure electrode impedances.
According to another aspect, alone or in combination with any other
aspect, the apparatus can include at least one analog input switch
that is operatively connected to the microcontroller, wherein the
microcontroller is configured to operate the analog input switch to
determine which of the recording electrodes are used to measure
feedback.
According to another aspect, alone or in combination with any other
aspect, the apparatus can include an analog front end circuit that
is operatively connected to the analog input switch, wherein the
analog front end is configured to facilitate sampling the recording
electrodes at a predetermined sample rate in order to determine
whether the feedback measured by the recording electrodes is
reliable. The sample rate can be 1,000-8,000 samples per
second.
According to another aspect, alone or in combination with any other
aspect, the microcontroller can be configured to initiate via the
analog front end a sampling window after energizing the stimulation
electrodes, wherein during the sampling window the recording
electrodes are used to measure feedback signals to determine
whether EMG data is present.
According to another aspect, alone or in combination with any other
aspect, the apparatus can include a radio for communicating
wirelessly with an external device for programming the
microcontroller, uploading/downloading data, and remotely
monitoring and/or controlling operation of the control unit.
According to another aspect, alone or in combination with any other
aspect, a method for treating overactive bladder can include
applying transcutaneous electrical stimulation to the tibial nerve
of a subject. The method can include positioning a plurality of
stimulation electrodes on a skin surface at a location between the
medial malleolus and the Achilles tendon proximate the tibial
nerve, the stimulation electrodes being spaced from each other in a
predetermined configuration. The method also can include
positioning one or more recording electrodes on a skin surface
remote from the stimulation electrodes at a location on the bottom
of the subject's foot near the abductor hallucis and the flexor
hallucis brevis muscles to record electromyogram (EMG) responses
that result from recruitment of the tibial nerve's motor fibers.
The method also can include stimulating the tibial nerve by
applying electrical stimulation pulses via a stimulation electrode
pattern selected from the plurality of stimulation electrodes
according to stimulation parameters under closed-loop control in
which EMG responses to the electrical stimulation pulses are
monitored via the recording electrodes and the stimulation
parameters are adjusted in response to the monitored EMG responses.
The method further can include, in response to detecting an
unacceptable condition of the recording electrodes, applying
electrical stimulation pulses via the stimulation electrode pattern
according to the stimulation parameters under open-loop control in
which the stimulation parameters are maintained without
adjustment.
According to another aspect, alone or in combination with any other
aspect, a system for treating overactive bladder by applying
transcutaneous electrical stimulation to the tibial nerve of a
subject can include a plurality of electrical stimulation
electrodes, the stimulation electrodes being spaced from each other
in a predetermined configuration, one or more recording electrodes,
a structure for supporting the stimulation electrodes and the
recording electrodes spaced apart from each other, and a control
unit for controlling the operation of the stimulation electrodes
and the recording electrodes. The control unit can be configured to
perform the method according to any of the aspects disclosed
herein, alone or in combination with any other aspect.
DRAWINGS
FIG. 1A illustrates a left-foot implementation of an electronic
medical device for delivering transcutaneous electrical stimulation
of peripheral nerves, according to a first example
configuration.
FIG. 1B illustrates a right-foot implementation of the electronic
medical device for delivering transcutaneous electrical stimulation
of peripheral nerves, according to the first example
configuration.
FIG. 2A is an inner surface plan view of the electronic medical
device of FIGS. 1A and 1B.
FIG. 2B is an outer surface plan view of the electronic medical
device of FIGS. 1A and 1B.
FIGS. 2C-E are outer surface plan views of the electronic medical
device of FIGS. 1A and 1B illustrating sequential steps in
preparing the device for use.
FIG. 3A illustrates a left-foot implementation of an electronic
medical device for delivering transcutaneous electrical stimulation
of peripheral nerves, according to a second example
configuration.
FIG. 3B illustrates a right-foot implementation of the electronic
medical device for delivering transcutaneous electrical stimulation
of peripheral nerves, according to the second example
configuration.
FIG. 4A is an inner surface plan view of components of the
electronic medical device of FIGS. 3A and 3B.
FIG. 4B is an outer surface plan view of the components of the
electronic medical device of FIGS. 3A and 3B.
FIG. 4C is an outer surface plan view, taken from a first side,
illustrating the components of FIGS. 4A and 4B assembled to form
the electronic medical device of FIGS. 3A and 3B.
FIG. 4D is an outer surface plan view, taken from a second side,
opposite the first side, illustrating the components of FIGS. 4A
and 4B assembled to form the electronic medical device of FIGS. 3A
and 3B.
FIG. 5 is a schematic block diagram of a control unit portion of
the electronic medical device.
FIG. 6 is a diagram illustrating example electrode arrangements for
portions of the electronic medical device.
FIG. 7 is a flow chart illustrating an example nerve localization
process implemented by the electronic medical device.
FIG. 8 is a series of charts illustrating examples of recorded EMG
responses to electrical nerve stimulation.
FIG. 9 is a flow chart illustrating an example open-loop and
closed-loop electrical nerve stimulation processes implemented by
the electronic medical device.
DESCRIPTION
An electronic medical device, a system including the medical
device, and a method for using the medical device, is configured to
apply transcutaneous electrical stimulation to peripheral nerves to
treat various medical conditions.
For example, the system can be used to stimulate the tibial nerve
(transcutaneous tibial nerve stimulation "TTNS") to treat medical
conditions associated with pelvic floor dysfunction, e.g.,
over-active bladder (OAB). In a TTNS implementation, the electronic
medical device applies electrical stimulation near the medial
malleolus, which activates both sensory and motor fibers in the
nerve. The activation of the sensory fibers of the tibial nerve
helps to treat the urge-related symptoms of OAB. The activation of
the motor fibers can, however, cause unwanted side effects, such as
toe twitch or spasm.
As another example, the system can be used to apply electrical
stimulation to the tibial nerve to treat sexual dysfunction. In
this manner, it is believed that tibial nerve stimulation could be
used to treat genital arousal aspects of female sexual
interest/arousal disorder by improving pelvic blood flow.
As another example, the system can be applied to the wrist area to
provide stimulation to the ulnar nerve and/or median nerve for pain
management in carpal tunnel syndrome, hypertension management, and
nerve conduction study/nerve injury diagnosis for median/ulnar
nerve neuropathy, etc.
The system and/or the device employed by the system can have a
variety of implementations. According to one implementation, the
electronic medical device (i.e., the electrodes, control unit,
wiring, etc.) can be fixed to a garment that is worn by the
subject. The garment can be tight or snug-fitting so as to maintain
sufficient contact between the subject's skin and can be configured
to position the electrodes at locations specific to the peripheral
nerves being stimulated. For example, to stimulate peripheral
nerves in the area of the foot or ankle, such as the tibial nerve
near the medial malleolus as described above, the garment can be in
the form of a sock, ankle brace, strap, sleeve, or other like
structure. For stimulating peripheral nerves on the leg, the
garment can be a brace, strap, or sleeve sized appropriately for
lower leg, knee, or upper leg positioning. For knee or ankle
positioning, the garment can be configured, e.g., with openings,
slots, or interconnected sections, to allow for bending with the
joint while maintaining electrode positioning and contact.
Similarly, for stimulating peripheral nerves on the hand, the
garment can be in the form of a glove, mitten, hand brace, or
sleeve. For stimulating peripheral nerves on the arm, the garment
can be a tight/snug fitting brace, strap, or sleeve (e.g.,
neoprene) that is sized appropriately for lower arm
(forearm/wrist), elbow, or upper arm positioning. For wrist and/or
elbow positioning, the sleeve can be configured, e.g., via
openings, slots, or interconnected sections, to allow for bending
with the joint while maintaining electrode positioning and
contact.
In keeping with the above, it will be appreciated that the manner
in which the electronic medical device can be secured or supported
on the subject can vary. It will also be appreciated that the
manner in which the electronic medical device is supported is not
critical, as long as contact between the electrodes and the
subject's skin is maintained, the positions of the electrode on the
subject are maintained, and that the aforementioned are achieved in
a manner that is comfortable to the subject.
Strap Implementation
FIGS. 1A-B illustrate a system comprising an example configuration
of the electronic medical device 10 for providing transcutaneous
electrical nerve stimulation, referred to herein as a
neurostimulator, supported on a subject 12. The neurostimulator 10
of FIGS. 1A-B includes a garment in the form of a strap 20 that
supports the neurostimulator and its components on the subject 12.
In the example configuration of FIGS. 1A-B, the strap 20 connects
the neurostimulator 10 to the subjects foot 14, with FIG. 1A
illustrating a left foot implementation, and FIG. 1B illustrating a
right foot implementation. In both instances, the strap 20 is
wrapped figure-eight style, with one loop extending around the foot
and one loop extending around the lower leg/ankle. Opposite end
portions of the strap 20 can be interconnected, e.g., via a buckle
or loop 22 and an end portion 24 of the strap that extends through
the loop, is folded over, and connected to itself with a hook and
loop fastener. The hook and loop fastener is shown in FIG. 2B and
includes a hook portion 26 and loop portion 28.
The strap 20 implementation of the neurostimulator 10 is
advantageous in that it is versatile and can be adapted to secure
the neurostimulator to a wide variety of locations on the subject
12. The strap 20 can easily be wrapped around the foot 14 and/or
ankle 16, as shown, and can also be wrapped around and secured to
any location along the length of the subject's leg 18, either in a
single loop or more than one loop, as the length of the strap
permits. At the knee, the strap 20 can be wrapped, for example, in
a figure-eight style in a manner similar to that illustrated in
FIGS. 1A and 1B.
Referring to FIGS. 2A-B, the neurostimulator 10 includes a several
of components that are secured or otherwise supported on the strap
20. The securement of these components can be achieved in a variety
of manners, such as by adhesives, stitching, mechanical fastening,
hook and loop fasteners, or a combination thereof.
The neurostimulator 10 includes stimulation electrodes 50 that are
arranged in one or more arrays 52 and positioned on an inner
surface 36 of the strap 20 at a widened end portion 30 of the
strap. The number of stimulation electrodes 50, the area covered by
the array 52, the electrode density (i.e., number of electrodes per
unit area) in the array, and the distribution or pattern of
electrodes within the array all can vary depending on the intended
application of the neurostimulator 10. Additionally, the
neurostimulator 10 can include more than one stimulation electrode
array 52 again, depending on the application. In the example
configuration of FIG. 2A, the stimulation electrode array 52
includes six stimulation electrodes 50 arranged in a generally
elongated kidney-shaped manner. The number and arrangement of the
stimulation electrodes 50, and the location/position of the
electrode array 52 on the strap 20 are by way of example only and
are by no means limiting.
In the example configuration of FIG. 2A, the stimulation electrodes
50 can be dry electrodes, in which case the neurostimulator 10 can
include a removable/replaceable stimulation gel pad 54 shaped and
sized to coincide with and cover the stimulation electrode array
52. In use, the gel pad 54 facilitates a strong, reliable
electrical connection between the stimulation electrodes 50 and the
subject's skin.
The neurostimulator 10 also includes dedicated recording electrodes
60 that are arranged in one or more arrays 62 and positioned on the
inner surface 36 of the strap 20 spaced from the stimulation
electrode array 52. The spacing between the stimulation electrodes
50 and the recording electrodes 60 can be important, as it can be
necessary to provide adequate distance between the electrodes so
that electrical stimulation signals can be separated or
distinguished from responses (e.g., neurological, muscular,
neuromuscular, etc.) to those electrical stimulation signals. This
facilitates utilizing responses to stimulation sensed by the
recording electrodes 60 as feedback in a closed-loop stimulation
control scheme, which is described in detail below.
The number of recording electrodes 60, the area covered by the
array 62, the electrode density (i.e., number of electrodes per
unit area) in the array, and the distribution or pattern of
electrodes within the array all can vary depending on the intended
application of the neurostimulator 10. Additionally, the
neurostimulator 10 can include more than one recording electrode
array 62 again, depending on the application. In the example
configuration of FIG. 2A, the recording electrode array 62 includes
four electrodes 60 arranged linearly in two parallel rows of two
electrodes. The number and arrangement of the recording electrodes
60, and the location/position of the electrode array 62 on the
strap 20 are by way of example only and are by no means
limiting.
In the example configuration of FIG. 2A, like the stimulation
electrodes 50, the recording electrodes 60 can also be dry
electrodes. Because of this, the neurostimulator 10 can also
include a removable/replaceable gel pad 64 shaped and sized to
coincide with and cover the recording electrode array 62. In use,
the gel pad 54 facilitates a strong, reliable electrical connection
between the recording electrodes 60 and the subject's skin.
Referring to FIG. 2B, the neurostimulator 10 also includes an
electronic control unit 70 that is operative to control the
application of transcutaneous electrical nerve stimulation via the
stimulating electrodes 50 and to receive stimulation feedback
gathered by the recording electrodes 60. The control unit 70 is
located at the widened end 30 of the strap 20 on an outer surface
38, opposite the inner surface 36, of the strap 20. The buckle 22
can be a portion of the control unit 70 or can be connected to the
control unit. In the example configuration of FIG. 2B, the control
unit 70 has a generally elongated kidney-shaped configuration
similar to that of the stimulating electrode array 52 and is
positioned on the outer surface 38 generally opposite the
stimulating electrode array. This is by no means necessary to the
design of the neurostimulator 10, as the shape and location of the
control unit 70 can vary.
In the example configuration of FIG. 2B, however, the shape and the
positioning of the control unit 70 is convenient. The control unit
70 is detachably connected to the remainder of the neurostimulator
10 via a plug-in or snap-in connector 72 (see FIG. 2B), which
receives a mating connector 74 (see FIG. 2D) on the control unit
70. FIG. 2B shows the control unit 70 connected to the
neurostimulator 20 via the connector 72, and FIG. 2C shows the
neurostimulator 20 with the control unit detached from the
connector and removed. Configuring the control unit 70 to be
detachable/removable allows the control unit to be utilized with
other neurostimulator configurations and also allows the strap 20
and the components remaining on the strap (e.g., the electrodes,
etc.) to be replaced when worn out, expired, or otherwise due for
replacement.
Advantageously, the stimulating electrode array 52 can be part of
an assembly in which the stimulating electrodes 50 can be mounted
on a substrate or housing 56 constructed, for example of plastic.
This substrate/housing 56 can itself be secured to the strap 20
(e.g., via adhesives, stitching, or mechanical fastening) to
thereby secure the stimulation electrode array 52 to be strap.
Forming the stimulating electrode array 52 in this manner
facilitates a precise arrangement and spacing of the stimulation
electrodes 50 and makes it easy to secure them to the strap 20.
The connector 72 can also be formed as a portion of the housing 56.
The connector 72 can be configured to protrude from a side of the
housing 56 opposite the stimulation electrodes 50. The connector 72
can, for example, extend through a hole in the strap 20 to position
the connector on or extending from the outer surface 38. When the
control unit 70 is connected to the connector 72, the strap 20 can
be positioned between the control unit and the portion of the
housing 56 supporting the stimulator electrode array 52.
The connector 72 can support a plurality of terminals for
electrically connecting the control unit 70 to the stimulation
electrodes 50 and the recording electrodes 60. Certain terminals in
the connector 72 can be electrically connected to the stimulation
electrodes 50 by wires or leads that are embedded within the
plastic housing material (e.g., via insert molding). Embedding the
leads in this manner helps maintain adequate spacing between the
conductors, which avoids the potential for shorts in the
circuitry.
Other terminals in the connector can be electrically connected to
the recording electrodes 60 by wires or leads 66 that are partially
embedded within the plastic housing material (e.g., via insert
molding) and pass through the housing 56, extending to the feedback
electrode arrays 62. Through this configuration, all of the
necessary electrical connections to the stimulation and recording
electrodes 50, 60 are made when the control unit 70 is installed on
the connector 72.
The neurostimulator 10 also includes electrode backing 80 that
facilitates safe storage and portability of the system. Fold lines
82, 84 shown in FIG. 2A indicate lines along which the
neurostimulator 10/strap 20 can be folded to place the device in
the stored condition. The steps involved in placing the
neurostimulator 10 in the stored condition are illustrated in FIGS.
2C-2E.
As shown in FIG. 2C, the control unit 70 is detached from the
housing 56. The control unit 70 is secured to the end portion 24 of
the strap 20 by the hook and loop fastener 26, 28. Next, as shown
in FIG. 2D, with the inner surface 36 facing up, the widened end
portion 38 is folded over along the fold line 82, which places the
stimulating electrode array 52 on a corresponding portion of the
electrode backing 80. Next, as shown in FIG. 2E, the strap 20 is
folded over along the fold line 84, which places the recording
electrode array 62 on a corresponding portion of the electrode
backing 80. This leaves the neurostimulator 10 in the stored
condition of FIG. 2E.
To use the neurostimulator 10, the strap 20 is simply unfolded and
the control unit 70 is connected to the housing 56 via their
respective connectors 72, 74. The hook and loop fastener 26, 28 can
be disconnected, the strap 20 wrapped around the appropriate
anatomy of the subject, and the fastener re-connected to attach
neurostimulator 10 to the subject. Conveniently, where the
neurostimulator 10 is configured for stimulating the tibial nerve
in the position illustrated in FIGS. 1A-B, the widened end 30 of
the strap 20 can include a visual alignment cue 90, such as a hole
in the strap, that becomes aligned with the medial malleolus of the
ankle when the stimulating electrodes are properly positioned.
Brace Implementation
FIGS. 3A-B illustrate a system comprising another example
configuration of an electronic medical device 110 for providing
transcutaneous electrical nerve stimulation, referred to herein as
a neurostimulator, supported on a subject 112. The neurostimulator
110 of FIGS. 3A-1B includes a garment in the form of a brace 120
that supports the neurostimulator and its components on the subject
112. In the example configuration of FIGS. 3A-B, the brace 120
connects the neurostimulator 110 to the subject's foot 114, with
FIG. 3A illustrating a left foot implementation, and FIG. 3B
illustrating a right foot implementation. In both instances, the
brace 120 has an upper portion 130 wrapped around the lower
leg/ankle and a lower portion 150 portion wrapped around the
foot/ankle. Each of these portions are secured to the subject via a
connection such as a hook and loop fastener.
The brace 120 implementation of the neurostimulator 10 is
advantageous in that it is versatile in its ability to position the
stimulating electrodes and recording electrodes at different
locations on the subject. For example, stimulating electrodes can
be positioned on the upper portion 130 of the brace 120 wrapped
around the ankle, and recording electrodes can be positioned on the
lower portion 150 of the brace wrapped around the foot. This can be
especially advantageous for closed-loop neurostimulation of the
tibial nerve. In this implementation, stimulating electrodes on the
upper portion 130 can be located between the medial malleolus and
the Achilles tendon to provide electrical stimulation to the tibial
nerve. Recording electrodes on the lower portion 150 can be located
on the bottom of the subject's foot, near the flexor muscles
(abductor hallucis and the flexor hallucis brevis) for the big toe
and can record the EMG signals that result from recruitment of the
tibial nerve's motor fibers.
As another advantage, the brace 120 is configured for placement at
or about a subject's joint and provides for movement of that joint.
While the brace 120 is illustrated as being applied at the
subject's ankle joint, it will be appreciated that the brace 120
can also be applied at the knee joint or elbow joint. Additionally,
positioning the brace 120 at a joint is not critical, as it can be
seen that the brace can be applied at any location along the
subject's arms or legs, size permitting.
The construction of the neurostimulator 110 is illustrated in FIGS.
4A-D. For the example configuration of FIGS. 4A-D the upper portion
130 and lower portion 150 of the strap 120 are separate components
that are interconnected by adjustment bands 122. The adjustment
bands 122 can allow for adjusting the spacing between the upper and
lower portions 130, 150, e.g., via a buckle or hook and loop
fastener, or the bands can be of a fixed size amongst a range of
sizes, e.g., x-small, small, medium, large, x-large, etc. The
respective sizes of the upper and lower portions 130, 150 can be
similarly sized. In fact, the upper portion 130 can itself be
composed of first and second portions 132, 134 connected by a band
136 that allows for adjusting the spacing between the upper and
lower portions 130, 150, e.g., via a buckle or hook and loop
fastener.
The upper portion 130 of the brace 120 includes a hook and loop
fastener composed of a hook portion 140 and a loop portion 142,
which are positioned opposite each other along an upper extent of
the upper portion. The upper portion 130 also includes opposite tab
portions 144 to which the adjustment tabs 122 (see, FIGS. 4C-D) are
connected, e.g., via stitching. Similarly, the lower portion 130 of
the brace includes a hook and loop fastener composed of a hook
portion 152 and a loop portion 154, which are positioned opposite
each other along a lower extent of the lower portion. The lower
portion 150 also includes opposite tab portions 156 to which the
adjustment tabs 122 (see, FIGS. 4C-D) are connected, e.g., via
stitching.
The neurostimulator 110 includes a several of components that are
secured or otherwise supported on the brace 120. The securement of
these components can be achieved in a variety of manners, such as
by adhesives, stitching, mechanical fastening, hook and loop
fasteners, or a combination thereof. FIGS. 4A and 4B illustrate the
neurostimulator 110 in a partially assembled condition, with the
electronic components of the neurostimulator mounted on the brace
120 prior to the first and second portions 132, 134 being
interconnected by the adjustment bands 122. This construction is
advantageous because it allows the electronic components of the
neurostimulator 110 to be assembled onto brace 120 while the upper
and lower portions 130, 150 lie flat. The lying flat illustration
of FIGS. 4A-B is for purposes of simplicity as it allows the upper
and lower portions 130, 150 to be illustrated lying flat. FIG. 4A
illustrates an inner surface 124 of the brace 120. FIG. 4B
illustrates an outer surface 126 of the brace 120.
The neurostimulator 110 includes stimulation electrodes 170 that
are arranged in one or more arrays 172 and positioned on the inner
surface 124 of the upper portion 130 of the brace 120. In the
example configuration illustrated in FIG. 4A, the stimulation
electrode arrays 172 are positioned on opposite sides of the
adjustment band 136 connecting the first and second portions 132,
134 of the upper portion 130. This arrangement can, for example,
allow the brace 130 implementation of the neurostimulator 110 to be
ambidextrous.
The number of stimulation electrodes 170, the area covered by the
stimulation electrode arrays 172, the electrode density (i.e.,
number of electrodes per unit area) in the arrays, and the
distribution or pattern of electrodes within the array all can vary
depending on the intended application of the neurostimulator 110.
In the example configuration of FIG. 4A, each stimulation electrode
array 172 includes six stimulation electrodes 170 arranged in a
generally rectangular manner in two rows of three electrodes. The
number and arrangement of the stimulation electrodes 170, and the
location/position of the electrode array 172 on the brace 120 are
by way of example only and are by no means limiting.
In the example configuration of FIG. 4A, the stimulation electrodes
170 can be dry electrodes, in which case the neurostimulator 110
can include one or more removable/replaceable stimulation gel pads
174 shaped and sized to coincide with and cover the stimulation
electrode array 172. In use, the gel pads 174 facilitate a strong,
reliable electrical connection between the stimulation electrodes
170 and the subject's skin.
The neurostimulator 110 also includes recording electrodes 180 that
are arranged in one or more arrays 182 and positioned on the inner
surface 124 of the lower portion 150 of the brace 120 at a location
spaced from the stimulation electrode arrays 172. The spacing
between the stimulation electrodes 170 and the recording electrodes
180 can be important, as it can be necessary to provide adequate
distance between the electrodes so that electrical stimulation
signals can be separated or distinguished from responses (e.g.,
neurological, muscular, neuromuscular, etc.) to those electrical
stimulation signals. This facilitates utilizing responses to
stimulation sensed by the recording electrodes 180 as feedback in a
closed-loop stimulation control scheme which, again, is described
in detail below.
The number of recording electrodes 180, the area covered by the
array 182, the electrode density (i.e., number of electrodes per
unit area) in the array, and the distribution or pattern of
electrodes within the array all can vary depending on the intended
application of the neurostimulator 110. In the example
configuration of FIG. 4A, there are two recording electrode arrays
182, each of which includes two recording electrodes 180 arranged
linearly. The number and arrangement of the recording electrodes
180, and the location/position of the electrode arrays 182 on the
brace 120 are by way of example only and are by no means
limiting.
In another implementation, the neurostimulator 110 can be
configured to include MMG sensors (e.g., accelerometers) for
sensing muscle movement as opposed to electrical activity. The
optional MMG sensors are illustrated in dashed lines at 186 in FIG.
4A. In this implementation, the MMG sensors 186 can be implemented
in addition to or in place of, the EMG electrodes 180. Implementing
the MMG 186 sensors along with the EMG sensors 180 can prove
beneficial in that the combination can provide additional
functionality. For example, the MMG sensor 186 can be used to
confirm the validity of an EMG measured feedback response.
Additionally, the MMG sensors 186 (or any other accelerometer for
that matter) can be used to verify that the subject in a resting,
i.e., not moving, condition prior to initiating a therapy
session.
In the example configuration of FIG. 4A, like the stimulation
electrodes 170, the recording electrodes 180 can also be dry
electrodes. Because of this, the neurostimulator 110 can also
include a removable/replaceable recording gel pad 184 shaped and
sized to coincide with and cover the recording electrode arrays
182. In use, the gel pad 184 facilitates a strong, reliable
electrical connection between the recording electrodes 180 and the
subject's skin.
Referring to FIG. 4B, the neurostimulator 110 also includes an
electronic control unit 200 that is operative to control the
application of transcutaneous electrical nerve stimulation via the
stimulating electrodes 170 and to receive stimulation feedback
gathered by the recording electrodes 180. The control unit 200 is
located on the outer surface 126 of the upper portion 130 adjacent
the adjustment band 136 and opposite one of the stimulating
electrode arrays 172 on the inner surface 124 of the upper portion.
In the example configuration of FIG. 4B, the control unit 200 has a
generally elongated racetrack-shaped configuration similar, to that
of the stimulating electrode arrays 172, although narrower. This is
by no means necessary to the design of the neurostimulator 110, as
the shape and location of the control unit 200 can vary.
In the example configuration of FIG. 4B, however, the shape and the
positioning of the control unit 200 is convenient. The control unit
200 can be detachably connected to the remainder of the
neurostimulator 110 via a plug-in or snap-in connector, such as by
a connector (not shown) that is similar or identical to the
connector associated with the control unit of the example
configuration of FIGS. 2A-D. Configuring the control unit 200 to be
detachable/removable allows the control unit to be utilized with
other neurostimulator configurations and also allows the brace 120
and the components remaining on the brace (e.g., the electrodes,
etc.) to be replaced when worn out, expired, or otherwise due for
replacement.
Advantageously, each stimulating electrode array 172 can be part of
an assembly in which the stimulating electrodes 170 can be mounted
on a substrate or housing 176 constructed, for example of plastic.
This substrate/housing 176 can itself be secured to the brace 120
(e.g., via adhesives, stitching, or mechanical fastening) to
thereby secure the stimulation electrode array 172 to be brace.
Forming the stimulating electrode array 172 in this manner
facilitates a precise arrangement and spacing of the stimulation
electrodes 170 and makes it easy to secure them to the brace
120.
In a manner similar or identical to that of the example
configuration of FIGS. 2A-D, the connector of each stimulating
electrode array 172 can also be formed as a portion of the housing
176. The connector can be configured to protrude from a side of the
housing 176 opposite the stimulation electrodes 170. The connector
can, for example, extend through a hole in the brace 120 to
position the connector on or extending from the outer surface 126.
When the control unit 200 is connected to the connector, the brace
120 can be positioned between the control unit and the portion of
the housing 176 supporting the stimulator electrode array 172.
Again, in a manner similar or identical to that of the example
configuration of FIGS. 2A-D, the connector can support a plurality
of terminals for electrically connecting the control unit 200 to
the stimulation electrodes 170 and the recording electrodes 180.
Certain terminals in the connector can be electrically connected to
the stimulation electrodes 170 by wires or leads that are embedded
within the plastic housing material (e.g., via insert molding).
Embedding the leads in this manner helps maintain adequate spacing
between the conductors, which avoids the potential for shorts in
the circuitry.
Other terminals in the connector can be electrically connected to
the recording electrodes 180 by wires or leads 184 that are
partially embedded within the plastic housing material (e.g., via
insert molding) and pass through the housing 176, extending to the
recording electrode arrays 182. Through this configuration, all of
the necessary electrical connections to the stimulation and
recording electrodes 170, 180 are made when the control unit 200 is
installed on the neurostimulator 110.
Referring to FIGS. 4C-D, the neurostimulator 110 is assembled by
connecting the first and second portions 132, 134 of the upper
portion 130 with the adjustment band 136. The upper and lower
portions 130, 150 are interconnected by two adjustment bands 122
that interconnect their respective tab portions 144, 156. This
completes the assembly of the neurostimulator 110, placing it in a
condition to be worn by the subject in the manner illustrated in
FIGS. 3A-B.
To use the neurostimulator 110, the brace 120 is simply unfolded
and the control unit 200 is connected to the housing 176 via the
connectors. The hook and loop fasteners 140, 142 and 152, 154 are
disconnected, the brace 120 wrapped around the appropriate anatomy
of the subject. In FIGS. 3A-B, the upper portion 130 is wrapped
around the lower leg/ankle 112 of the subject, and the lower
portion 150 is wrapped around the foot 114 of the subject. The hook
and loop fasteners 140, 142 and 152, 154 are re-connected to attach
neurostimulator 110 to the subject. Conveniently, where the
neurostimulator 110 is configured for stimulating the tibial nerve
in the position illustrated in FIGS. 3A-B, the upper portion 130 of
the brace 120 can include visual alignment cues 210, such as holes
in the brace, that become aligned with the medial malleolus of the
ankle when the stimulating electrodes 170 are properly
positioned.
Control Unit Configuration
The control units 70, 200 of the example configurations of the
neurostimulator 10, 110 of FIGS. 1A-4D can have a variety of
configurations. An example configuration for the control units 70,
110 is shown in FIG. 5. Referring to FIG. 5, the control unit 70,
200 includes a microcontroller 220 powered by a primary or
rechargeable battery 222 via a battery protection and charging
circuit 224. The circuit 224 offers battery protection typical for
a medical device, such as over-current and over-voltage protection,
under-voltage protection, and a charging controller. An external
cable or charging cradle 226 charges the battery 222 via the
circuit 224. Alternatively, the battery 222 can be charged
wirelessly, e.g., via a wireless charging cradle. A pushbutton 228
cycles on/off power to the control unit 70, 200.
The battery protection and charging circuit 224 also marshals power
to a high voltage power supply circuit 230, a digital power supply
circuit 232, and an analog power supply circuit 234. The
high-voltage power supply circuit 230 is used to provide a
stimulation compliance voltage to the output stage's current
sources and sinks. Since this device is a transcutaneous
stimulator, it can require a compliance voltage in the range of
about 40-200 V or more in order to provide the necessary current to
stimulate the tibial nerve. For this embodiment, a compliance
voltage of 120 volts is used for the compliance voltage.
A radio controller 240, such as a Bluetooth.RTM. or Zigbee.RTM.
radio controller, provides a communication input to the
microcontroller 220 for functions such as programming the control
unit 70, 200, uploading/downloading data, and
monitoring/controlling the neurostimulator 10, 110 during use. The
radio controller 240 could, for example, pair the microcontroller
to an enabled device, such as a smartphone, tablet, or computer,
executing software that enables the user to monitor or otherwise
control the operation of the neurostimulator 10, 110. The
microcontroller 220 controls the operation of indicators 242, such
as LEDs, that indicate the state or condition of the control unit
70, 210. The microcontroller 220 can control an accelerometer 244,
which can provide input to determine whether the neurostimulator
10, 110, and thus the subject, is moving or at rest.
The microcontroller 220 is responsible for controlling the
stimulation output, measuring the electrode impedance, and
processing the EMG response. The microcontroller 220 runs software
for performing these functions, including decision-making
algorithms to allow the device to provide the desired therapy. The
microcontroller 220 controls the operation of an amplitude control
circuit 250, a timing control circuit 252, and a digital-to-analog
converter (DAC) 254. By "circuit," it is meant that these functions
can be implemented in any desired manner, e.g., through discrete
components, integrated circuits, or a combination thereof. The
amplitude control circuit 250, timing control circuit 252, and DAC
254 drive a stimulator output stage 260, which provides stimulator
output signals (e.g., pulse-width-modulated "PWM" output signals)
to one or more analog output switches 262. The output switch(es)
262 are operatively connected to a port 280 comprising a plurality
of terminals (E1-E8 in FIG. 5) that facilitates connecting the
control unit 70, 200 to the stimulator and recording electrodes,
for example, via the leads 66, 184 (see, FIGS. 2A and 4B,
respectively). Through this connection via the leads 66, 184, the
stimulator output stage 260 can be operatively connected to the
stimulator electrodes 50, 170.
The microcontroller 220 receives electrode impedance values via an
impedance measurement circuit 264 that is operatively connected to
the stimulator output stage 260. The microcontroller 220 also
receives electrode feedback values (e.g., F-wave and M-wave values)
via an analog front end 270 that is operatively connected to one or
more analog input switches 272. The input switch(es) 272 are also
operatively connected to the terminals/port 280 and can thereby
receive feedback from the recording electrodes 60, 180 that
facilitates connecting the control unit 70, 200 to the stimulator
and recording electrodes, for example, via the leads 66 (see, FIG.
2A) or 184 (see, FIG. 4B).
The impedance measurement circuit 264 allows for measuring the
impedance of the electrodes. It is important to measure the
impedance often, in case one or more of the electrodes begins to
lift from the skin. There are two potential hazards related to
electrode lifting that should be mitigated. First, if an electrode
is partially lifted from the skin, the surface area of the
electrode that is in contact with the skin is reduced and the
current density of the stimulation current is increased, which can
be unsafe. Second, if an active electrode is completely lifted from
the skin, a brief but large amount of energy can be delivered to
the tissue when the electrode makes contact with the skin, which
can result in pain.
Electrode impedances measured via the impedance measurement circuit
264 can also be used as an additional input for a closed-loop
stimulation optimization algorithm.
The stimulator output stage 260 provides the current to the
stimulating electrodes via the output switch 262. Each channel of
the output stage includes a current source and current sink, which
allows each channel to provide either a positive or negative
current to the tissue through the corresponding stimulation
electrode(s) 50, 170. In this configuration, each current source
and sink can have independently programmable amplitude control 250
and timing control 252, which provides the capability to "steer"
the current applied via the stimulation electrodes 50, 170, as
described below. The programmable range can vary depending on the
application, and is selected to be capable of achieving the desired
nerve recruitment. In an example configuration, the current sources
can have a programmable range from zero to +20 milliamperes (mA),
and the current sinks can have a programmable range from zero to
-20 mA.
As shown in FIG. 5, the analog output switches 262 and input
switches 272 can both be operatively connected to each of the
terminals E1-E8. Through operation of the switches 262, 272 as
commanded by the microcontroller 220, the identity or role of the
terminals, i.e., output terminal or input/feedback terminal, can be
actively identified. This allows the microcontroller 220 to
selectively identify, activate, and deactivate electrodes in a
desired pattern, order, combination, etc., according to the
particular therapy regimen being applied. This also allows the
therapy to be tailored, for example, in response to signals
received from the recording electrodes.
Control Overview
According to one example implementation, the neurostimulator 10,
100 described above can control the application of stimulation
therapy according to two general phases: nerve localization and
stimulation delivery. These two phases work synergistically to
provide the functionality set forth in the following
paragraphs.
During the nerve localization phase, the target peripheral nerve
structure, e.g., the tibial nerve, is localized when the
neurostimulator 10, 100 is donned and activated. In the nerve
localization phase, the neurostimulator 10, 100 implements a
process in which the following functions are performed: Ramping up
stimulation energy across various electrode patterns. Monitoring
EMG response after each stimulation pulse. Determining the
electrode pattern and stimulation parameters that optimally
activate the target peripheral nerve.
During the stimulation delivery phase, electrical stimulation is
delivered to the target peripheral nerve structure using the
electrode pattern(s) and stimulation parameters determined during
the nerve localization phase. In the stimulation delivery phase,
the neurostimulator 10, 100 implements a process in which the
following functions are performed: Deliver stimulation pulses to
the target peripheral nerve. Continuously optimize the delivery of
stimulation pulses, which includes: Monitoring EMG response after
each stimulation pulse. Monitoring electrode impedance. Adjusting
either the electrode pattern (current-steering) or stimulation
energy to optimize recruitment of the tibial nerve. Automatically
stopping stimulation at the end of the therapy session.
The nerve localization and stimulation delivery phases are
described in more detail in the following sections.
Nerve Localization
In practice, the control unit 110 can be programmed with a set of
electrode patterns that identify which stimulation electrode 50,
170 in an electrode array 52, 172 are active, and also the polarity
or type, i.e., anode (+) or cathode (-) assigned to the electrode.
FIG. 6 illustrates an example configuration for an electrode array
52, 172 and a chart illustrating an example set of electrode
patterns. In the example illustrated in FIG. 6, the electrode array
52, 172 has eight electrodes 50, 170, identified at E1-E8, and the
chart identifies ten different electrode patterns (patterns 1-10)
for the electrode array. For each electrode pattern, each electrode
is identified as being a cathode (C), anode (A), or inactive
(blank). Thus, for example, in pattern 3, electrodes E1 and E2 are
cathodes, electrodes E5 and E6 are anodes, and electrodes E3, E4,
E7, and E8 are inactive. While there are a large number of patterns
that are possible with an eight-electrode array, the patterns can
effectively be narrowed down to a shorter list, such as the
illustrated 10 patterns or more, depending on the nerve under
recruitment.
The neurostimulator 10, 110 can be configured to perform a nerve
localization routine to determine which of the electrode patterns
should be utilized on a subject. In the example configuration of
FIG. 6, the electrode array 52, 172 can be specifically designed,
i.e., shaped and electrodes positioned, to stimulate the tibial
nerve in the region between the medial malleolus and the Achilles
tendon. The electrode array 52, 172 can be configured to perform
stimulation on this or other regions where peripheral nerve
stimulation is desired.
In the example configuration of FIG. 6, the electrode array 52, 172
is curved to allow the medial malleolus to be used as a placement
guide. Also, the array can be symmetrical so that it can be placed
on either ankle. The electrode arrangement within the array must be
configured to capture the tibial nerve, meaning that the nerve must
pass below or between at least one pair of electrodes. If the
tibial nerve passes outside the extents of the array, activation of
the tibial nerve requires much higher stimulation energies, or it
may not be possible to activate the tibial nerve at all.
The purpose of using an array for stimulation (as opposed to a
single pair of electrodes) is to create an optimized stimulation
field for recruiting the target (e.g., tibial) nerve. If the
stimulation field is too small, the nerve will not be recruited and
therapy will not be delivered. If the stimulation field is too
large, too many motor neurons will be recruited resulting in
undesired effects, such as pain, twitching, or muscle spasm. In
order to optimize the stimulation field, the ability to steer
current using multiple electrodes if preferred. For example,
electrode pattern 8 assigns electrodes E3 and E4 as anodes and
electrodes E7 and E8 as cathodes. Viewing the arrangement of these
electrodes 50, 170 on the array 52, 172, it can be seen that the
use of this electrode pattern could be effective on a nerve path
that passes directly adjacent or between these electrode pairs.
By selecting the appropriate stimulation electrodes 50, 170 from
the stimulation electrode arrays 52, 172, and varying the amplitude
and polarity of the current applied via the selected electrodes,
the electric field applied to the subject can be shaped so that the
current is steered to the target nerves. By shaping the field, the
neurostimulator 10, 100 can automatically adjust to day-to-day
donning and placement variability for a given subject. Current
steering also allows the neurostimulator 10, 100 to work across a
subject population with wide anatomical variation, for example
providing a shallow field for subjects with nerves that are
superficial to the skin, or a penetrating field for subjects with
nerves that are deep. In the illustrated example configurations,
the stimulation electrode arrays 52, 152 include six electrodes.
Any number of stimulation electrodes greater than one can be used.
In general, the "field steering" capability of the neurostimulator
10, 100 increases with the number of stimulating electrodes 50, 170
that are included.
Because there will be session-to-session variability in the
location of the stimulating electrode array 52, 172 due to the
don/doff process, as well as variability in skin/tissue impedance,
providing open-loop stimulation applying rigid pre-programmed
stimulation parameters could be disadvantageous, often providing
too little or too much stimulation energy to recruit the nerve.
Advantageously, the nerve localization algorithm is executed at the
beginning of each therapy session to determine which of the
preprogrammed electrode patterns will be most effective.
FIG. 7 illustrates a flowchart showing the method or process 300
implemented by the nerve localization algorithm. The steps in the
process 300 are not meant to be exclusive, i.e., other steps can be
included. Nor is the process 300 intended to be strictly followed
in terms of the order shown in FIG. 7 or described herein. The
process 300 illustrates steps, perhaps a minimum, necessary to
localize the peripheral nerve that is to be stimulated.
It should be noted here that, the process 300 is a closed-loop
algorithm that utilizes feedback recorded via the recording
electrodes 60, 180 to make determinations and/or adjust settings.
As such, the process 300 relies on utilization of the feedback to
determine which of the electrode patterns effectively achieves
nerve recruitment. Specifically, the process 300 relies on feedback
from the recording electrodes 60, 180 to provide indication of EMG
response feedback. Alternatively, the process 300 can rely on
accelerometers to provide MMG response feedback.
Referring to FIG. 7, the process 300 begins at step 302, where an
impedance measurement is performed in order to determine which, if
any, of the electrodes E1-E8 have open or prohibitively high
impedance. This step 302 can be considered an integrity check for
the electrodes 50, 170 in the array 52, 172 to determine if any of
the electrodes in the array are not sufficiently contacted with the
skin. If any of the electrodes in the array are determined to be
performing in a substandard manner, indicated by displaying an open
(infinitely high) or sufficiently high impedance, those electrodes
and the electrode patterns that utilize those electrodes can be
eliminated from use.
For example, in the example of FIG. 6, it can be seen from row 2
that electrode E6 has high impedance. In this instance, electrode
patterns 3, 6, 7, and 9 are eliminated form use in the current
therapy session. Alternatively, the algorithm could instruct the
control unit to provide some indication to the user, such as an
alarm or display, to re-position or adjust the electrodes to see if
contact can be improved.
To avoid interfering with stimulation and EMG measurement, the
integrity check at step 302 can be completed in a short amount of
time, such as 25 milliseconds or less. Also, the impedance
measurement can be conducted so as to cause little or no sensation
in the subject's skin. Therefore, the excitation current for
performing the integrity check should be low-amplitude, such as 1
mA or less. For the integrity check 302, the impedance value at
each electrode is not critical. Instead, determining whether the
impedance is below a certain threshold is adequate.
Additionally, conditions other than high or low impedance can be
determined in this integrity check. For example, indicators such as
dry/wet contact checks, whole/brittle/fractured contact checks,
contact surface area checks, and contact reflectance checks can be
made during the connectivity evaluation. Sensors, such as don/doff,
stretch, strain, bending or contact sensors (via electrical,
optical or mechanical means) can also be used for conducting the
connectivity evaluation. These sensors could also be incorporated
into a buckle, clasp, snap, hook/eye or zipper feature.
Once the integrity check is performed, the process 300 proceeds to
step 304 where the first electrode pattern (that hasn't been
eliminated by the integrity check) is loaded. The process 300 then
proceeds to step 306 where the neurostimulator 10, 110 generates
stimulation pulse(s) using the electrode pattern loaded in step
304. The process 300 proceeds next to step 310, where a
determination is made as to whether the stimulation pulses
generated at step 306 elicited an EMG response, i.e., feedback
measured via the recording electrodes. Step 310 can additionally or
alternatively determine whether there is a MMG response where the
feedback devices include accelerometer(s).
If, at step 310, EMG (or MMG) is not detected, the process 300
reverts to step 314, where a new electrode pattern is loaded. The
process 300 then proceeds to step 306, as described above. If, at
step 310, EMG (or MMG) is detected, the process 300 proceeds to
step 312, where the electrode pattern is added according to pattern
selection rules. The process 300 then proceeds to step 316, where a
determination is made as to whether the current electrode pattern
is the last electrode pattern in the list.
The pattern selection rules at step 312 for adding an electrode
pattern can be defined to prioritize electrode patterns identified
as being the best suited to recruit the target nerves. These
pattern selection rules may be implemented as follows: If one
pattern is significantly better than the others (e.g., as
determined from the EMG data, see below), that pattern should be
used as the primary pattern moving forward. If two or three
patterns are roughly equivalent, any one of the patterns can be
used as the primary pattern. Moving forward, this pattern can be
switched to other ones if the nerve recruitment displayed by the
current primary pattern begins to diminish. If the nerve
recruitment for a particular pattern begins to diminish and
increasing the stimulation parameters does not fix the problem,
similar patterns can be re-introduced to the algorithm.
If, at step 316, it is determined that the current electrode
pattern is not the last pattern in the list, the process 300
reverts to step 314, where a new electrode pattern is loaded. The
process 300 then proceeds to step 306, as described above. If, at
step 316, it is determined that the current electrode pattern is
the last pattern in the list, this indicates that the pattern list
is complete. The process 300 proceeds to step 320 where the
stimulation parameters for the electrode patterns in the pattern
list are optimized. At step 320, the stimulation parameters (e.g.,
frequency, amplitude, pattern, duration, etc.) are updated to
optimize the nerve recruitment for each pattern. The process 300
then reverts back to the initial step at 302 and proceeds as
described above. If the recruitment for a given electrode pattern
improves, the stimulation parameters are kept. If not, they revert
back to previous values. This process repeats itself until the
pattern list is filled with electrode patterns optimized for nerve
recruitment.
From the above, it will be appreciated that the nerve localization
process 300 determines which of the electrode patterns to utilize
and which to discard for any given stimulation therapy session, and
then optimizes the stimulation parameters for the utilized
patterns. The execution of this process 300 is fast. During
execution, the neurostimulator 10, 110 applies stimulation therapy
pulses via the stimulating electrodes 50, 170 and monitors for EMG
responses via the recording electrodes 60, 180 after each
pulse.
The analog front end circuit 270 can replace traditional EMG
measurement circuitry such as a filter, amplifier, rectifier,
and/or integrator. The control unit 110 utilizes the analog
front-end circuit 270 to sample the recording electrodes at a
predetermined sample rate, such as 1,000-8,000 samples per second.
The EMG sampling window will begin after the stimulation pulse is
finished, and the window will last for a predetermined brief
period, such as 8-90 milliseconds. The resulting EMG data,
comprised of M-wave or F-wave or both, will be analyzed using a
Fast Fourier Transform (FFT) technique that clearly shows if EMG is
present.
To execute the process 300 of FIG. 7, the neurostimulator 10, 110
monitors for electromyogram (EMG) signals via the recording
electrodes 60, 180 in response to stimulation applied via the
stimulation electrodes 50, 170. FIG. 8 illustrates examples of the
EMG responses that can be recorded, which include: No EMG Response,
F-wave Response, M-wave Response, and M and F-wave Response. In the
example where no EMG response is recorded, the stimulation pulse
artifact can be seen on the left, with no response following. In
the example where an M-wave response is recorded, the stimulation
pulse artifact can be seen on the left, followed by the M-wave at
about 6 to 10 ms post-stimulation. In the example where an F-wave
response is recorded, the stimulation pulse artifact can be seen on
the left, followed by the F-wave responses at about 50 to 55 ms
post-stimulation. In the example where both an M-wave and F-wave
responses are recorded, the stimulation pulse artifact can be seen
on the left, followed by the M-wave and F-wave at 6 to 10 ms and
about 50 to 55 ms post-stimulation, respectively. These response
times could change slightly, depending on a variety of factors,
such as the hydration and/or salinity of the subject tissue, the
arrangement and spacing of the electrodes, and the characteristics
of the stimulation signals.
For each of the four recorded response scenarios, FIG. 8 also
illustrates a corresponding Fast Fourier Transform (FFT) results
for the raw post-artifact signal. The FFT results are calculated by
the microcontroller 220 and are used in the process 300 to
determine whether an EMG response is present (see, step 310 in FIG.
7).
Stimulation Delivery
The neurostimulator 10, 110 can apply stimulation therapy using an
open-loop control scheme, a closed-loop control scheme, or a
combination of open-loop and closed-loop control schemes, depending
on the control algorithm programmed into the microcontroller 220.
For open-loop control, the control units 70, 200 can apply
electrical stimulation via the stimulation electrodes 50, 170
according to settings (frequency, amplitude, pattern, duration,
etc.) without regard to any feedback measured via the recording
electrodes 60, 180. This is not to say that feedback is not
measured, just that, in an open-loop control scheme, the feedback
is not used to inform or control the algorithm executed by the
microcontroller 220 to control the application of stimulation
therapy. In a closed-loop control scheme, the neurostimulator 10,
110 implements a control algorithm in which feedback from the
recording electrodes 60, 180 informs and helps control the
application of stimulation therapy.
FIG. 9 illustrates by way of example a process 400 by which the
neurostimulator 10, 110 controls the application of electrical
nerve stimulation using the electrode pattern(s) identified by the
nerve localization process 300 of FIG. 7. The stimulation control
process 400 can employ both open-loop and closed-loop control, with
closed-loop steps or portions of the process being illustrated in
solid lines and open-loop steps or portions being illustrated in
dashed lines. Ideally, the process 400 will proceed with
closed-loop control, as it is able to utilize feedback to optimize
the application of stimulation therapy.
The process 400 begins at step 402, where the impedances of the
recording electrodes 60, 180 are checked. If, at step 404, it is
determined that the recording electrode impedances are too high
(e.g., resulting in unavailable or unreliable feedback), the
process 400 then shifts to open-loop mode (see dashed lines) and
proceeds to step 412, where a delay is implemented. The purpose of
delay 412 is to assist in maintaining a constant stimulation
period, meaning that the duration of delay 412 should be equal to
the duration of closed-loop step 406. After completing delay 412,
the process 400 proceeds to step 414, where the stimulation
electrode impedances are checked.
At step 404, if the impedances of the recording electrodes are
acceptable, the process 400 remains in closed-loop mode and
proceeds to step 406, where samples are obtained via the recording
electrodes to check for significant noise or voluntary EMG
responses. At step 410, if noise or EMG are present, the feedback
is considered unreliable and the process 400 shifts to open-loop
mode and proceeds to step 414. At step 410, if significant noise or
voluntary EMG is not present, the feedback is considered reliable
and the process 400 remains in closed-loop mode and proceeds to
step 414.
At step 414, regardless of whether the process is in open-loop mode
or closed-loop mode, the impedances of the stimulation electrodes
50, 170 are checked. At step 416, if the stimulation electrode
impedances are acceptable, the process 400 proceeds to step 420 and
the neurostimulator 10, 110 generates stimulation pulses, which are
applied via the stimulation electrodes using the optimal electrode
pattern, as determined by the nerve localization process 300 (see
FIG. 7). If, at step 416, the stimulation electrode impedances are
too high, the process 400 proceeds to step 420 and the
neurostimulator 10, 110 generates stimulation pulses that are
applied via the stimulation electrodes using an alternative
electrode pattern selected from the pattern list determined by the
nerve localization process 300. In either case, after generating
the stimulation pulse using the optimal pattern (step 420) or the
alternative pattern (step 422), the process 400 proceeds to step
424.
At step 424, the process 400 implements a pre-recording delay to
allow time for the electrical stimulation applied at step 420 or
422 to elicit an EMG response. As discussed above, these delays can
be relatively short, so the delay at step 424 can, likewise, be
short, e.g., 5 ms or less. If the process 400 is in open loop mode,
it proceeds to step 432, where a further delay is implemented. This
delay 432 should match the duration of closed-loop steps 426 and
430 so that a constant stimulation period is maintained. If the
process 400 is in closed-loop mode, it proceeds to step 426 and
checks for feedback via the recording electrodes 60, 180. The
process 400 then proceeds to step 430, where any detected EMG
feedback signals are recorded and analyzed.
At this point, regardless of whether the process 400 is in
open-loop mode (step 432) or closed-loop mode (step 430), the
process proceeds to step 434, where a determination of whether the
number of stimulation pulses applied in the current therapy session
has reached a predetermined number (N). If the predetermined number
(N) of pulses have not yet been applied, the process proceeds to
step 436, the stimulation amplitude is maintained at the current
level, and the process 400 reverts back to step 402, where the
impedance of the recording electrodes is checked and the process
400 repeats. If, at step 434, the predetermined number (N) of
pulses has been reached, the process 400 proceeds to step 440.
At step 440, if the process 400 in open-loop mode, the process
proceeds to step 442, the stimulation amplitude is maintained at
the current level, and the process 400 reverts back to step 402,
where the impedance of the recording electrodes is checked and the
process 400 repeats. At step 440, if the process 400 is not in
open-loop mode (i.e., is in closed-loop mode), the process proceeds
to step 444, where a determination is made as to whether the EMG
recorded at step 430 is below a predetermined window, i.e., below a
predetermined range of acceptable EMG values. If the EMG is below
the predetermined window, the process 400 proceeds to step 446,
where the stimulation amplitude is increased for the next pulse, if
permitted. The process 400 then reverts back to step 402, where the
impedance of the recording electrodes is checked and the process
400 repeats with the increased stimulation amplitude.
If, at step 444, the EMG is not below the window, the process 400
proceeds to step 450 where a determination is made as to whether
the EMG is above the predetermined window. If the EMG is above the
predetermined window, the process 400 proceeds to step 452, where
the stimulation amplitude is decreased for the next pulse. The
process 400 then reverts back to step 402, where the impedance of
the recording electrodes is checked and the process 400 repeats
with the decreased stimulation amplitude. If, at step 450, the EMG
is not above the predetermined window, the EMG is determined to be
within the predetermined window and the process 400 proceeds to
step 454, where the stimulation amplitude is maintained at the
current level for the next pulse. The process 400 then reverts back
to step 402, where the impedance of the recording electrodes is
checked and the process 400 repeats.
While aspects of this disclosure have been particularly shown and
described with reference to the example aspects above, it will be
understood by those of ordinary skill in the art that various
additional aspects may be contemplated. A device or method
incorporating any of the features described herein should be
understood to fall under the scope of this disclosure as determined
based upon the claims below and any equivalents thereof. Other
aspects, objects, and advantages can be obtained from a study of
the drawings, the disclosure, and the appended claims.
* * * * *